Stirling engine

ABSTRACT

A stirling engine includes a flow path that communicates a working space of the stirling engine and outside of the stirling engine. A working gas is supplied from the outside of the stirling engine to the working space via the flow path based on a differential pressure of the working space and the outside of the stirling engine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stirling engine, and more particular,to a stirling engine suitable for increasing a working gas pressure ofthe stirling engine.

2. Description of the Related Art

In recent years, stirling engines which have an excellent theoreticalthermal efficiency attract attention as an external combustion enginewhich collects exhaust heat from an internal combustion engine mountedon a vehicle such as an automobile, a bus, and a truck, as well asexhaust heat from factories.

Japanese Patent Application Laid-Open No. S64-342 discloses an outputcontrol apparatus for a stirling engine which includes a connection tubethat connects a working space and a crankcase and an accumulator.

An efficient increase in the working gas pressure of the stirling engineis desired. In particular, when a pressuring device such as apressurizing pump is to be used, reduction of energy used for thepressurization is desired.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is toprovide a stirling engine which is capable of efficiently increasing aworking gas pressure.

A stirling engine according to one aspect of the present inventionincludes a flow path that communicates a working space of the stirlingengine and outside of the stirling engine. A working gas is suppliedfrom the outside of the Stirling engine to the working space via theflow path based on a differential pressure of the working space and theoutside of the stirling engine.

In the stirling engine, the flow path is provided with a filter thatprevents an impurity from entering the working space from the outsideinto via the flow path.

In the stirling engine, the working gas is supplied from the outside ofthe stirling engine into the working space via the flow path when apressure of the working gas in the working space is lower than a meanvalue of the pressure of the working gas in the working space in onecycle.

In the stirling engine, a working gas of an atmospheric pressure issupplied from the outside of the stirling engine into the working spacevia the flow path.

The stirling engine further includes a pressurized fluid supplying unitthat is connected to the flow path at the outside of the stirling engineto supply a pressurized working gas.

In the stirling engine, the pressurized fluid supplying unit is a pistonpump.

In the stirling engine, the piston pump is provided so that a phase ofan intra-cylindrical pressure of the piston pump is of an opposite phasewith the pressure of the working gas in the working space.

The stirling engine further includes a communication tube thatcommunicates the working space with a crankcase of the stirling engine;and an opening and closing unit that opens and closes the communicationtube. The opening and closing unit is put into a state where thecommunication tube is open when the pressure of the working gas in theworking space is higher than a pressure of the crankcase.

In the stirling engine, the flow path is provided so that the flow pathcommunicates the working space at a low temperature side of the stirlingengine and the outside of the stirling engine.

The stirling engine further includes a cylinder; and a piston thatreciprocates in the cylinder. The piston reciprocates in the cylinderwhile keeping cylinder airtight with an air bearing provided between thecylinder and the piston.

The stirling engine further include an approximately linear mechanismthat is connected to the piston so that the approximately linearmechanism makes an approximately linear motion when the pistonreciprocates in the cylinder.

A hybrid system according to another aspect of the present inventionincludes a stirling engine according to the present invention; and aninternal combustion engine of a vehicle. The stirling engine is mountedon the vehicle and a heater of the stirling engine is provided toreceive a heat from an exhaust system of the internal combustion engine.

In the hybrid system, the stirling engine includes at least twocylinders, and a heat exchanger including a cooler, a regenerator, andthe heater. The heat exchanger is configured so that at least a portionof the heat exchanger forms a curve to connect the two cylinders. Thecurve is adapted to connect upper portions of the two cylinders where adimension of an inner diameter of the exhaust tube of the internalcombustion engine is approximately same with a distance between an endportion of the heater and an uppermost portion of the heater.

In the hybrid system, the stirling engine is attached to the vehicle sothat pistons of the stirling engine reciprocate substantiallyhorizontally.

In view of the foregoing, an object of the present invention is toprovide a stirling engine which is capable of efficiently increasing aworking gas pressure.

According to the stirling engine of the present invention, an efficientincrease of the working gas pressure is allowed.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a structure of a stirling engineaccording to a first embodiment of the present invention;

FIG. 2 is a graph of intra-cylindrical pressure prior to pressurizationof a crankcase in the stirling engine according to the first embodimentof the present invention;

FIG. 3 is a graph of intra-cylindrical pressure after the pressurizationof the crankcase in the stirling engine according to the firstembodiment of the present invention;

FIG. 4 is a schematic sectional view of a stirling engine according to asecond embodiment of the present invention;

FIG. 5 is a schematic sectional view of a structure of a stirling engineaccording to a third embodiment of the present invention;

FIG. 6A is a graph of intra-cylindrical pressure prior to closing of avalve in the stirling engine according to the third embodiment of thepresent invention, and FIG. 6B is a graph of the intra-cylindricalpressure after the closing of the valve in the stirling engine accordingto the third embodiment of the present invention;

FIG. 7 is a graph of intra-cylindrical pressure prior to pressurizationof a crankcase in a stirling engine according to a fourth embodiment ofthe present invention;

FIG. 8 is a schematic sectional view of a structure of the stirlingengine according to the fourth embodiment of the present invention;

FIG. 9 is a schematic sectional view of a structure of the stirlingengine according to a fifth embodiment of the present invention;

FIG. 10 is a graph of intra-cylindrical pressure of the stirling engineand the intra-cylindrical pressure of a piston pump in the stirlingengine according to the fifth embodiment of the present invention;

FIG. 11 is a sectional view of a basic common structure of the stirlingengine according to the embodiments of the present invention;

FIG. 12 is a plan view of an attachment state of an internal combustionengine and the stirling engine of the embodiments of the presentinvention;

FIG. 13 is a graph of the intra-cylindrical pressure of the stirlingengine according to the embodiments of the present invention; and

FIG. 14 is an explanatory diagram of approximately linear mechanismapplied to the stirling engine according to the embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, stirling engines according to embodiments of thepresent invention will be described in detail with reference to theaccompanying drawings.

The embodiments which will be described below relate to pressurizationof a working space, i.e., increase in working gas pressure, andpressurization of a crankcase 41. First, a common structure to allembodiments will be described followed by descriptions of pressurizationof the working space (i.e., increase in working gas pressure) and thecrankcase 41 according to the respective embodiments.

FIG. 11 is a front sectional view of a stirling engine of theembodiments. As shown in FIG. 11, the stirling engine of the embodimentsis a stirling engine 10 of α-type (two-piston type) and provided withtwo power pistons 20 and 30. Two power pistons 20 and 30 are arranged inparallel in line. A piston 31 of the power piston 30 on a lowtemperature side is arranged so that the piston 31 moves with a phasedifference of 90° in a crank angle with respect to a piston 21 of thepower piston 20 on a high temperature side as shown in FIG. 13.

A working fluid heated by a heater 47 flows into a space (expansionspace) in an upper section of a cylinder 22 (hereinafter referred to asa high temperature side cylinder) of the power piston 20 on the hightemperature side. A working fluid cooled by a cooler 45 flows into aspace (compression space) in an upper section of a cylinder 32(hereinafter referred to as a low temperature side cylinder) of thepower piston 30 on the low temperature side.

A regenerator (regenerative heat exchanger) 46 stores heat while theworking fluid flows back and forth between the expansion space and thecompression space. In other words, when the working fluid flows from theexpansion space to the compression space, the regenerator 46 receivesheat from the working fluid, whereas the stored heat is transferred tothe working fluid when the working fluid flows from the compressionspace to the expansion space.

The reciprocating flow of the working fluid caused by the reciprocatingmovement of two pistons 21 and 31 (also referred to as expansion piston21 and compression piston 31 hereinbelow), changes the ratio of theworking fluid in the expansion space of the high temperature sidecylinder 22 and the compression space of the low temperature sidecylinder 32, as well as the total volume of the fluid in the spaces tocause pressure variations. When the relation between the pressure leveland the positions of the cylinders 21 and 31 is to be compared, thepressure is substantially higher when the expansion piston 21 is in alower position than in a higher position, whereas the pressure issubstantially lower when the compression piston 31 is in a lowerposition than in a higher position. Thus, the expansion piston 21performs a positive work (expansion work) of a substantial amount to theoutside, whereas the compression piston 31 needs to receive a work(compression work) from the outside. The expansion work is partlyutilized for the compression work and the rest is extracted as an outputvia a driving shaft 40.

The stirling engine of the embodiments is employed with a main engine200, a gasoline engine or an internal combustion engine, for example, ina vehicle as shown in FIG. 12, thereby forming a hybrid system. In otherwords, the stirling engine 10 is an exhaust heat collecting unit whichutilizes exhaust gas from the main engine 200 as a heat source. With theheater 47 of the stirling engine 10 placed in an exhaust tube 100 of themain engine 200 of the vehicle, heat energy collected from the exhaustgas heats up the working fluid thereby starting up the stirling engine10.

Since the stirling engine 10 of the embodiments is placed in a limitedspace in the vehicle, e.g., the heater 47 is housed in the exhaust tube100, the overall structure thereof is preferably made compact toincrease the degree of freedom in installation. To this end, in thestirling engine 10, two cylinders 22 and 32 are not arranged in a “V”configuration but placed in a parallel in-line layout.

The heater 47 is arranged inside the exhaust tube 100, so that a side ofthe heater 47 on the side of high temperature side cylinder is locatedat an upstream side 100 a (a side closer to the main engine 200) of theexhaust gas where exhaust gas of a relatively high temperature flows inthe exhaust tube 100, whereas a side of the heater 47 on the side of thelow temperature side cylinder 32 is located at a downstream side 100 b(a side farther from the main engine 200) where exhaust gas of arelatively low temperature flows. Such arrangement intends to heat upthe side of the heater 47 on the side of the high temperature sidecylinder 22 to a higher level.

Each of the high temperature side cylinder 22 and the low temperatureside cylinder 32 is formed in a cylindrical shape and supported by abase plate 42 which serves as a baseline. In the embodiments, the baseplate 42 serves to provide a reference position for respectivecomponents of the stirling engine 10. With such structure, the relativelocation accuracy of respective components of the stirling engine 10 canbe secured. In addition, the base plate 42 can be used as a referencefor attachment of the stirling engine 10 to the exhaust tube 100(exhaust path) which provides exhaust heat to be collected.

The base plate 42 is fixed to a flange 100 f of the exhaust tube 100 viaa heat insulating material (spacer not shown). The base plate 42 is alsofixed to a flange 22 f provided in a side face (outer peripheralsurface) 22 c of the high temperature side cylinder 22. The base plate42 is also fixed to a flange 46 f provided in a side face (outerperipheral surface) 46 c of the regenerator 46.

The exhaust tube 100 is attached to the stirling engine 10 via the baseplate 42. The stirling engine 10 is attached to the base plate 42 sothat an end face (an upper face of a top portion 22 b) of the hightemperature side cylinder 22 where the heater 47 is connected, and anend face (a top face 32 a) of the low temperature side cylinder 32 wherethe cooler 45 is connected are substantially parallel with the baseplate 42. Alternatively, the stirling engine 10 is attached to the baseplate 42 so that the base plate 42 is parallel with a rotation shaft ofa crank shaft 61 (or the driving shaft 40) or so that a central axis ofthe exhaust tube 100 is parallel with the rotation shaft of the crankshaft 61. Thus, the stirling engine 10 can be readily attached to theexhaust tube 100 of an existing type without a major change in design.As a result, the stirling engine 10 can be attached to the exhaust tube100 without impoverishing the characteristics such as performance,mountability and a noise-reducing feature, of the internal combustionengine of a vehicle from which the exhaust gas is collected. Inaddition, since the stirling engine 10 of the same specification can beattached to a different exhaust tube only with a change in specificationof the heater 47, the versatility of the stirling engine can beenhanced.

The stirling engine 10 is arranged horizontally in a space adjacent tothe exhaust tube 100 which is placed under a floor of the vehicle. Inother words, the stirling engine 10 is arranged so that the axes of thehigh temperature side cylinder 22 and the low temperature side cylinder32 are substantially parallel with the floor (not shown) of the vehicle.Two pistons 21 and 31 reciprocate horizontally. In the embodiments, anupper dead point side and a lower dead point side of two pistons 21 and31 are referred to as an upper direction and a lower direction,respectively, for the simplicity of description.

A higher output can be obtained when a mean pressure (Pmean describedlater) of the working fluid is higher since a differential pressure atthe same temperature difference caused by the cooler 45 and the heater47 is larger. Hence, as described above, the working fluid in theworking space of the high temperature side cylinder 22 and the lowtemperature side cylinder 32 is maintained in a high pressure.

The pistons 21 and 31 are formed in a cylindrical shape. Between theouter peripheral surface of pistons 21 and 31 and the inner peripheralsurface of the cylinders 22 and 32, a minute clearance of a few tenmicrometers (μm) is provided. The working fluid (air) of the stirlingengine 10 is present in the clearance. The pistons 21 and 31 aresupported by an air bearing 48 so that the pistons do not contact withthe cylinders 22 and 32, respectively. Hence, piston rings are notprovided around the pistons 21 and 31, and lubricant which is generallyused together with the piston ring is not employed. To the innerperipheral surface of the cylinders 22 and 32, however, an antifrictionis fixed. Though resistance of the air bearing 48 toward slidingmovement caused by the working fluid is originally extremely low, theantifriction is provided for further resistance reduction. As describedabove, the air bearing 48 serves to maintain the expansion space and thecompression space airtight with the working fluid (air) and seals theclearance without the piston ring and the lubricant.

The heater 47 includes a plurality of heat transfer tubes (tube group)47 t, each of which is formed generally in a U-shape. A first endportion 47 ta of each heat transfer tube 47 t is connected to the upperportion (top portion) (end face at the side of a top face 22 a) 22 b ofthe high temperature side cylinder 22. A second end portion 47 tb ofeach heat transfer tube 47 t is connected to an upper portion (end faceat the side of the heater 47) 46 a of the regenerator 46. The reason whythe heater 47 is formed generally in U-shape as described above will bedescribed later.

The regenerator 46 includes a heat storage material (matrix not shown)and a regenerator housing 46 h that houses the matrix. Since theregenerator housing 46 h accommodates the working fluid of highpressure, the regenerator housing 46 h is formed as a pressure-tightcontainer. The regenerator 46 here includes laminated metallic meshes asthe matrix.

The regenerator 46 has to meet the following conditions to realize theabove described functions. The regenerator 46 is required to have a highheat transfer performance, a high heat storage capacity, a low flowresistance (flow loss, pressure loss), a low heat conductivity in adirection of the working fluid flow, and a large thermal gradient. Themetallic mesh may be formed of stainless steel. When the working fluidpasses through each of the laminated metallic meshes, heat of theworking fluid is transferred and stored in the metallic mesh.

A connecting portion (shape of a cross section) of the heater 47 withthe high temperature side cylinder 22 is formed in the same shape andsize with the shape of an opening (perfect circle) of the upper portion(a connecting portion with the heater 47) of the high temperature sidecylinder 22. Similarly, a connecting portion of the heater 47 with theregenerator 46 is formed in the same shape and size with the upper faceof the regenerator 46. Thus, the cross sections of the heater 47 and theregenerator 46 are formed in the same shape and size with the openingsof the high temperature side cylinder 22 and the low temperature sidecylinder 32, respectively. With such a structure, resistance of a flowpath (flow resistance) of the working fluid is decreased.

The crank shaft 61 is rotatably supported by a bearing with respect tothe crankcase 41. In the embodiments, a counterweight 90 is provided ona side of the high temperature side cylinder 22. The position of thecounterweight 90 is selected so as to minimize the influence on thevertical size of the overall stirling engine 10. A sufficient space canbe secured in the space on a side of the high temperature side cylinder22.

Next, a reason why the heater 47 is formed generally in U-shape (curvedshape) as described above will be described.

The heat source of the stirling engine 10 is the exhaust gas of the mainengine 200 of the vehicle as described above and not a heat sourcededicated exclusively to the stirling engine. Hence, the amount of heatto be obtained is not very large. The stirling engine 10 is required tostart up with a small amount of heat obtained from the exhaust gas, ofapproximately 800° C., for example. Thus, the heater 47 of the stirlingengine 10 is required to efficiently receive the heat from the exhaustgas in the exhaust tube 100.

A volume of a heat exchanger which includes the heater 47, theregenerator 46, and the cooler 45 is a void volume, which does notdirectly affect the output. When the volume of the heat exchangerincreases, the output of the stirling engine 10 decreases. On the otherhand, when the heat exchanger is made small in volume, the heat exchangebecomes difficult and the received amount of heat decreases, whereby theoutput of the stirling engine 10 is decreased. Hence, to realize boththe decrease in the void volume and the increase in the received amountof heat, the efficiency of the heat exchanger is required to beenhanced. In other words, the efficient receipt of heat by the heater 47is required.

To realize the efficient heat receipt from the exhaust gas in theexhaust tube 100 and the efficient heat exchange, the whole structure ofthe heater 47 is required to be accommodated in the exhaust tube 100 injust proportion, and the cooler 45 is required to be located outside theexhaust tube 100 to avoid receiving the heat from the exhaust gas.Hence, when the flange 100 f where the exhaust tube 100 is attached tothe stirling engine 10 is taken as a reference, a position of attachmentof the low temperature side cylinder 32 is lower than a position ofattachment of the high temperature side cylinder 22 at least by theheight of the cooler 45. Thus, a position of the compression spaceformed in the upper section of the low temperature side cylinder 32 islower than the position of the expansion space formed in the uppersection of the high temperature side cylinder 22, and an upper deadpoint of the compression piston 31 is lower than a position of an upperdead point of the expansion piston 21.

In the embodiments, piston pins 60 a and 60 b are connected to pistons21 and 31, respectively, with extensions (piston supports) 64 a and 64 bof different sizes to change the positions of the upper dead points ofthe pressurizing piston 31 and the expansion piston 21. Since theposition of the upper dead point of the expansion piston 21 is higherthan the upper dead point of the compression piston 31, the extension 64a connected to the expansion piston 21 is longer than the extension 64 bconnected to the compression piston 31 by the difference in the heightof position of the upper dead point.

In the embodiments, the expansion piston 21 and the compression piston31 are formed so that the lengths thereof are equal. In other words, thedistances between the upper faces of pistons 21 and 31 and connectionpoints 21 c and 31 c with the extensions 64 a and 64 b of the pistons 21and 31, respectively, are made equal. Therefore, the extensions 64 a and64 b are formed in different lengths to arrange the upper dead points ofthe piston 21 and 31 at different positions. Alternatively, theextensions of the expansion piston and the compression piston may beformed in the same length, and the lengths of the expansion piston andthe compression piston may be made different. Thus, the positions of theupper dead points of the expansion piston and the compression piston canbe made different. A technical advantage of such structure where thevertical length of the expansion piston itself is made longer than thatof the compression piston itself will be described below.

For the suppression of deterioration in the efficiency of the stirlingengine 10, a space outside the expansion space in the high temperatureside power piston 20 and a space outside the compression space in thelow temperature side power piston 30, i.e., a space around the crankshaft 61 in each of the high temperature side power piston 20 and thelow temperature side power piston 30 is required to be maintained at aroom temperature. Hence, secure sealing must be provided between thehigh temperature side cylinder 22 and the expansion piston 21, andbetween the low temperature side cylinder 32 and the compression piston31, so that the working fluid of a high temperature in the expansionspace will not flow into the space around the crank shaft 61 at the sideof the high temperature side power piston 20 and the working fluid of alow temperature in the compression space will not flow into the spacearound the crank shaft 61 on the side of the low temperature side powerpiston 30. As described later, the air bearing 48 is employed to achievesuch sealing.

On the other hand, since the top portion 22 b and the side face 22 c ofthe high temperature side cylinder 22 are housed inside the exhaust tube100 as described above, the upper portion of the high temperature sidecylinder 22 and the upper portion of the expansion piston 21 thermallyexpand. Then, the sealing might not be secured in a section where theupper portions of the high temperature side cylinder 22 and theexpansion piston 21 expand. To avoid such inconvenience, the expansionpiston 21 and the high temperature side cylinder 22 may be formed longerin the vertical direction to provide a thermal gradient in verticaldirection of the expansion piston 21. Then, the secure sealing can beguaranteed with the section not affected by the thermal expansion, i.e.,the lower portion of the expansion piston 21. Further, since the sealingbetween the high temperature side cylinder 22 and the expansion piston21 is provided with the lower portion of the expansion piston 21, i.e.,the section not affected by the thermal expansion, the high temperatureside cylinder 22 may be formed longer in the vertical direction toguarantee the sufficient moving distance for the sealing section and tosufficiently pressurize the expansion space.

The structure of the embodiments is preferable regardless of the type ofthe heat source, since such structure allows efficient reception of heatfrom the heat source and efficient heat exchange by providing the heaterwith a large heat transfer area for the reception of heat energy and thecooler which can be arranged in a position not heated.

In particular, when the exhaust heat is to be utilized, the heat energyis generally supplied by the exhaust gas through a tube. Then, an areawhere the heat can be received (tube interior, for example) isrelatively limited. In such case, the structure of the stirling engine10 as described above is particularly preferable since it provides alarge heat transfer area and a cooler is arranged in a position notheated. A technical advantage of the structure of the stirling engine 10will be further described below.

A smaller void volume (the cooler, the regenerator, and the heater) ispreferable as described above. In addition, when the void volume sectionhas a curved shape, the resistance in the flow path becomes large whenmany such curved portions exist whereas the resistance in the flow pathincreases when the curvature of the curved portion is small. In otherwords, with the pressure loss of the working fluid considered,preferably a single curved portion with a large curvature is provided.Though the heater 47 is generally in U-shape, the heater 47 has only onecurved portion. In addition, the cooler 45 is formed to have a curvedportion for the downsizing of the stirling engine 10 (reduction invertical dimension), whereby the structure with the features asdescribed above is realized.

In addition, as shown in FIG. 11, the curvature of the void volumeportion in the embodiments is set according to the arrangement where theupper portions of two cylinders 22 and 32 arranged in parallel in lineare coupled, and the vertical distance between the top portion 22 b ofthe high temperature side cylinder 22 and the upper face 46 a of theregenerator 46 arranged approximately in the same plane to suppress theincrease in flow resistance of the working fluid in the exhaust tube 100and the upper inner face of the exhaust tube 100 is set to a height hwhich is approximately equal to the distance between the end portions 47ta and 47 tb and the uppermost portion of a central portion 47 c of theheater 47. To secure a large contact area with the fluid heat sourcesuch as the exhaust gas in a limited space such as the interior of theexhaust tube 100, the curved shape as described above is desirable.

With such advantages considered, the heater in the void volume portionis preferably formed in a curved shape such as a U-shape or a J-shape,so that the entirety of the heater is housed in a limited space(heat-receiving space) receiving the heat from the heat source such asthe interior of the exhaust tube and a maximum area to receive the heatfrom the heat source can be secured and the resistance of the flow pathis minimized in the heat-receiving space.

To minimize the resistance of the working fluid in the flow path, theregenerator 46 is arranged linearly (along the same axis) along adirection of extension (direction of axis) of the low temperature sidecylinder 32. Thus, the regenerator 46 connected to a second end portion47 tb of the heater 47 is arranged along the direction of extension ofthe low temperature side cylinder 32. A first end portion 47 ta of theheater 47 is seamlessly connected to the upper portion of the hightemperature side cylinder 22. Thus, the heater 47 has portions extendingalong the directions of extension of the high temperature side cylinder22 and the low temperature side cylinder 32 at least at the sides of thefirst end portion 47 ta and the second end portion 47 tb of the heater47, and the central portion 47 c of the heater 47, in many cases, has acurved shape as described above.

Due to the technical reasons as described above, the heater 47 is formedin a curved shape between two cylinders 22 and 32 which are arranged inparallel in line. Thus, the heater 47 has a curved portion connectingtwo cylinders 22 and 32.

Next, a sealing structure of a piston/cylinder section and a mechanismof a piston/crank section will be described.

As described above, since the heat source of the stirling engine 10 isthe exhaust gas from the internal combustion engine of the vehicle, theobtainable amount of heat is limited and the stirling engine 10 isrequired to function in the range of obtainable heat amount. Hence, inthe embodiments, the internal friction of the stirling engine 10 isminimized as far as possible. In the embodiments, to eliminate thefriction loss by the piston ring which generally produces the largestfriction loss among the internal friction in the stirling engine, thepiston ring is eliminated from the structure. In place of the pistonring, the air bearing 48 is provided between the cylinders 22 and 32 andthe pistons 21 and 31, respectively.

The air bearing 48 can significantly reduce the internal friction of thestirling engine 10 since the sliding resistance thereof is extremelysmall. Since the cylinders 22 and 32 and the pistons 21 and 31 aresecured airtight also with the air bearing 48, the working fluid of ahigh temperature would not leak out at the time of expansion andcontraction.

The air bearing 48 utilizes the air pressure generated in the minuteclearances between the cylinders 22 and 32 and the pistons 21 and 31 tosupport the pistons 21 and 31 in a floating position. The air bearing 48of the embodiments has a clearance of a few ten micrometers (μm) indiameter between the cylinders 22 and 32 and the pistons 21 and 31. Torealize the air bearing that supports a material in a floating position,a mechanism may be structured to have a high air pressure section(thereby creating pressure gradient). Alternatively, ahighly-pressurized air may be sprayed as described later.

The air bearing used in the embodiments is not the type to which thehighly-pressurized air is sprayed but an air bearing which has the sameconfiguration as an air bearing employed between a cylinder and a pistonfor a glass injection syringe for medical application.

In addition, since the use of the air bearing 48 eliminates thelubricant which is used for the piston ring, the deterioration of theheat exchanger (the regenerator 46 and the heater 47) of the stirlingengine 10 is not caused by the lubricant. Here, as far as theinconvenience accompanying the use of the lubricant and the piston ring,such as the sliding resistance, can be eliminated, any air bearingsexcluding one type of fluid dynamic bearing called an oil bearing whichuses oil may be employed other than the air bearing 48.

Alternatively, a static pressure air bearing may be employed between thepistons 21 and 31 and the cylinders 22 and 32 of the embodiments. Thestatic pressure air bearing floats a material (the pistons 21 and 31 inthe embodiments) by spraying a pressurized fluid and utilizing agenerated static pressure. Alternatively, a dynamical pressure airbearing may be employed instead of the static pressure air bearing.

When the pistons 21 and 31 reciprocate inside the cylinders 22 and 32with the use of the air bearing 48, an accuracy of linear motion shouldbe maintained below the clearance in diameter of the air bearing 48.Further, since the loading capacity of the air bearing 48 is small, aside force applied by the pistons 21 and 31 is required to besubstantially zero. In other words, since the air bearing 48 has alittle capacity to bear the force applied in a direction of a diameterof the cylinders 22 and 32, i.e., a lateral direction or a thrustdirection, the accuracy of linear motion of the pistons 21 and 31 withrespect to axes of the cylinders 22 and 32 is required to beparticularly high. In particular, since the air bearing 48 of theembodiments which floats and supports the material with the air pressureproduced by the minute clearance has a lower pressure bearing capacityin the thrust direction compared with the type of bearing that spraysthe highly-pressurized air, an accordingly higher accuracy of linearmotion of the piston is required.

Hence in the embodiments, a grasshopper mechanism 50, i.e., anapproximately linear link, is employed for the piston/crank section. Thegrasshopper mechanism 50 achieves the same accuracy of linear motion ina smaller mechanism compared with other approximately linear mechanism(the Watt mechanism, for example), thereby providing a more compactoverall system. In particular, since the stirling engine 10 of theembodiments is installed in a limited space, for example, the heater 47thereof is housed in the exhaust tube of the vehicle, a more compactoverall system increases a degree of freedom in installation. Inaddition, the grasshopper mechanism 50 can achieve the same accuracy oflinear motion in a lighter mechanism compared with other mechanisms, andis advantageous in terms of fuel consumption. Further, the grasshoppermechanism 50 has a relatively simple structure and is easy to build(manufacture/assemble).

FIG. 14 shows a schematic structure of a piston/crank mechanism of thestirling engine 10. In the embodiments, the piston/crank mechanismadopts a common structure for the high temperature side power piston 20and the low temperature side power piston 30. A description will begiven hereinbelow only on the low temperature side power piston 30 and adescription on the high temperature side power piston 20 will beomitted.

As shown in FIGS. 14 and 11, a reciprocating movement of thepressurizing piston 31 is transferred to the driving shaft 40 via aconnecting rod 109 (65 a and 65 b) and converted into a rotationmovement. The connecting rod 109 is supported by the approximatelylinear mechanism 50 shown in FIG. 14 to make the low temperature sidecylinder 32 reciprocate linearly. With the approximately linearmechanism 50 supporting the connecting rod 109, the side force Fproduced by the compression piston 31 is substantially zero. Hence, eventhe air bearing 48 with a small load bearing capacity can sufficientlysupport the compression piston 31.

Next, pressurization of the working fluid in the working space of thestirling engine 10 and pressurization of the crankcase 41 will bedescribed.

As described above, a high output can be obtained when the mean workinggas pressure Pmean of the working fluid in the working space of thestirling engine 10 is maintained at a high level. In addition, in thestirling engine 10 of the embodiments, the pressure in the crankcase 41is raised up to the mean working gas pressure Pmean inside the cylinderof the stirling engine 10. The increase in the pressure in the crankcase41 up to the mean working gas pressure Pmean inside the cylinder of thestirling engine 10 is intended to eliminate the need of a high strengthof the components (piston, for example) of the stirling engine 10 in thedesign thereof.

In other words, when the pressure of the crankcase 41 is at the level ofthe mean working gas pressure Pmean inside the cylinder of the stirlingengine 10, the differential pressure of the intra-cylindrical pressureof the stirling engine 10 and the pressure inside the crankcase 41 canbe suppressed to the differential pressure between the maximum (orminimum) intra-cylindrical pressure and the mean working gas pressurePmean at the maximum. Thus, with the suppression of differentialpressure between the intra-cylindrical pressure of the stirling engine10 and the pressure of the crankcase 41, the strength of the componentsof the stirling engine 10 can be low. When the components are notrequired to have a high strength, lighter components can be realized.

In the stirling engine 10 of the embodiments, the crankcase 41 ispressurized prior to a normal operation up to the mean working gaspressure Pmean inside the cylinder of the stirling engine 10.

First, pressurization of the working fluid in the working space of thestirling engine 10 and pressurization of the crankcase 41 will bedescribed according to a first embodiment.

Here, the mean working gas pressure Pmean mentioned above will bedescribed with reference to FIG. 13.

FIG. 13 shows changes of the top position of the high temperature sidepiston 21 and the top position of the low temperature side piston 31. Asdescribed above, the phase difference is provided so that the lowtemperature side piston 31 moves 90° later by the crank angle than thehigh temperature side piston 21. In FIG. 13, a combined wave W of a waveform of the high temperature side piston 21 and a wave form of the lowtemperature side piston 31 represents the intra-cylindrical pressure(intra-cylindrical pressure P of FIG. 2). In FIG. 13, the referencecharacter “Pmean” indicates the mean working gas pressure which is amean value of the intra-cylindrical pressure.

FIG. 2 shows an initial state of the crankcase 41 of the stirling engine10 according to the first embodiment prior to the pressurization. Thegraph of FIG. 2 shows the combined wave W where the vertical axisrepresents the intra-cylindrical pressure and the horizontal axisrepresents the crank angle. As shown in FIG. 2, prior to thepressurization of the crankcase 41, the pressure Pc of the crankcase 41(=mean working gas pressure Pmean) is equal to the atmosphere pressurePo.

In the first embodiment, changes in the pressure (intra-cylindricalpressure P) of the working fluid of the stirling engine 10 is utilizedfor the increase in the pressure Pc of the crankcase 41 as describedlater. In general, the intra-cylindrical pressure P moves from a lowerrange than the mean working gas pressure Pmean (from a second half ofthe expansion process through a first half of the compression process)up to a higher range than the mean working gas pressure Pmean (from asecond half of the compression process through a first half of theexpansion process) repeatedly as indicated by the reference character Win FIG. 13. In the first embodiment, the pressure Pc of the crankcase 41is increased together with the mean working gas pressure Pmean with theuse of the changes in the intra-cylindrical pressure P.

In the foregoing, the lower range of the intra-cylindrical pressure Pthan the mean working gas pressure Pmean corresponds with a period inone cycle of the expansion/pressurization of the working fluid where theworking gas pressure is lower than the mean Pmean of the working gaspressure in the pertinent cycle, whereas the higher range of theintra-cylindrical pressure P than the mean working gas pressure Pmeancorresponds with a period where the working gas pressure is higher thanthe mean Pmean of the working gas pressure in the pertinent cycle. Thesame applies below.

FIG. 1 is a schematic diagram of a structure of the first embodiment. InFIG. 1, the same components with the components shown in FIG. 11 areindicated with the same reference characters and the detaileddescription thereof will not be repeated.

As shown in FIG. 1, a path 71 is provided at a position corresponding toa position around a lower dead point of the piston 31 in the lowtemperature side cylinder 32 to communicate with the compression space(inside the cylinder) of the low temperature side cylinder 32. In thepath 71 a filter 72 is provided. The path 71 serves to let the fluid(working fluid) of the atmospheric pressure Po flow from the outside ofthe stirling engine 10 into the cylinder. The path 71 is configured tolet the fluid flow (let the pressure transfer) only in one direction,i.e., from the outside into the cylinder.

The filter 72 serves to prevent any impurities from entering thecylinder from outside of the stirling engine 10 via the path 71. Asdescribed above, the path 71 is not provided to the high temperatureside cylinder 22, but is connected to the low temperature side cylinder32. Since the thermal difference between the outside of the stirlingengine 10, i.e, of a room temperature, and the working fluid is smallerfor the compression space of the low temperature side cylinder 32 thanfor the expansion space of the high temperature side cylinder 22, thepath 71 is connected to the low temperature side cylinder 32 to causerelative decrease in the thermal loss at the time the outside air comesinto the cylinder.

As shown in FIG. 2, when the intra-cylindrical pressure P drops belowthe atmospheric pressure Po (becomes a negative pressure) (from thesecond half of the expansion process through the first half of thecompression process), the fluid (air) of the atmospheric pressure Poenters into the cylinder via the path 71, and is pressurized through thecompression process of the stirling engine 10 (from the second half ofthe compression process in particular). The pressure (fluid) pressurizedin the compression process is transferred to the crankcase 41 via theclearance CL between the cylinders 32 and 22 and the pistons 31 and 21.Thus, the crankcase 41 is pressurized.

With the repetition of the above described process, the mean working gaspressure Pmean (which is equal to the pressure Pc in the crankcase 41)rises above the atmospheric pressure Po and the mean working gaspressure Pmean attains the level of the pressure Pc of the crankcase 41as shown in FIG. 3. When the stirling engine 10 operates in the raisedstate of the mean working gas pressure Pmean, the stirling engine 10 canattain a high output.

Next, with reference to FIG. 4, a pressurizing of the working fluid inthe working space of the stirling engine 10 and a pressurizing of thecrankcase 41 according to a second embodiment will be described.

FIG. 4 shows a schematic structure of a stirling engine according to thesecond embodiment. The same component with the first embodiment shown inFIG. 1 is indicated with the same reference character and thedescription thereof will not be repeated.

The second embodiment is different from the first embodiment in that acheck valve 73 is provided in the path 71. The check valve 73 is formedso that the check valve 73 opens only when a pressure at the side of thetip portion 71 a of the path 71 is higher than a pressure at the side ofa base portion 71 b thereof. Hence, the path 71 has a structure totransfer the pressure (working fluid) only in the direction from theoutside into the cylinder. In addition, the second embodiment includes apath 81 which connects the interior of the cylinder of the stirlingengine 10 with the crankcase 41.

According to the second embodiment, when the intra-cylindrical pressureP of the stirling engine 10 is lower than the atmospheric pressure Po,the fluid of the atmospheric pressure Po of the outside flows into thecylinder via the path 71 and pressurized in the compression process ofthe stirling engine 10. The pressure increased in the compressionprocess is transmitted to the crankcase 41 via the path 81. Thus, thecrankcase 41 is pressurized. With the repetition of the process, themean working gas pressure Pmean (pressure Pc in the crankcase 41) risesabove the atmospheric pressure Po and the mean working gas pressurePmean attains the level of the pressure Pc of the crankcase 41 as shownin FIG. 3 similar to the first embodiment.

In the first embodiment, when the sealing pressure of the minuteclearance between the cylinders 32 and 22 and the pistons 31 and 21 ishigh, the pressure (fluid) increased in the compression process is notreadily transferred to the crankcase 41 via the clearance CL (or thetransfer takes time). In the second embodiment, however, since thepressure is transferred to the crankcase 41 via the path 81, suchinconvenience will not occur.

Next, a pressurizing of the working fluid in the working space of thestirling engine 10 and a pressurizing of the crankcase 41 according to athird embodiment will be described with reference to FIGS. 5 to 6B.

FIG. 5 shows a schematic structure of the third embodiment. The samecomponent with the second embodiment shown in FIG. 4 is indicated withthe same reference character and the detailed description thereof willnot be repeated. The third embodiment is different from the secondembodiment in that a check valve 82 and a valve 83 are provided in thepath 81. The check valve 82 is formed so that the check valve opens onlywhen a pressure at the tip portion 81 a on the side of the cylinder ishigher than a pressure at the tip portion 81 b on the side of thecrankcase 41.

According to the third embodiment, the crankcase 41 is pressurized viathe path 81 when the intra-cylindrical pressure P is higher than thepressure Pc of the crankcase 41 while the valve 83 is open as shown inFIG. 6A. When the intra-cylindrical pressure P is lower than theatmospheric pressure Po, the fluid of the atmospheric pressure Po flowsinto the cylinder via the path 71. With the repetition of the process,the crankcase 41 is pressurized and the valve 83 eventually closes. Thenas shown in FIG. 6B, the mean working gas pressure Pmean rises up to thelevel of the pressure Pc of the crankcase 41.

When the volume of the working fluid in the cylinder and the volume ofthe crankcase 41 are compared, the volume of the working fluid issmaller than the volume of the crankcase 41. Hence, the mean working gaspressure Pmean rises up to the pressure Pc of the crankcase 41. In thethird embodiment, with the check valve 82 and the valve 83 in the path81, the flow of the fluid from the side of the crankcase 41 into thecylinder via the path 81 can be securely suppressed.

Next, a pressurizing of the working fluid of the working space of thestirling engine 10 and a pressurizing of the crankcase 41 according to afourth embodiment will be described with reference to FIGS. 7 and 8.

In the first to the third embodiments described above, the pressure Pcof the crankcase 41 is increased with the use of the atmosphericpressure Po. In the fourth embodiment, the pressure Pc of the crankcase41 is increased with the use of auxiliary machinery such as a pressuresource like a pressurizing pump. In the fourth embodiment, reduction inenergy consumption of the auxiliary machinery which is used to increasethe pressure Pc of the crankcase 41 and downsizing of the installationscale are intended.

In the fourth embodiment, the reduction in energy consumption of theauxiliary machinery and the downsizing of the installation scale arerealized through the use of a pumping function accompanying thepressurization/expansion of the stirling engine 10 which is describedabove with reference to the first to the third embodiments.

FIG. 8 shows a structure of a stirling engine according to the fourthembodiment. The same component with the first embodiment shown in FIG. 1is indicated with the same reference character and the detaileddescription thereof will not be repeated. In the fourth embodiment, abranch path 75 is connected to the path 71 so that the branch path 75diverts from the path 71. The branch path 75 is provided with apressurizing pump 91 and a tank 92 arranged at a downstream side of thepressurizing pump 91. The tank 92 serves to store the fluid pressurizedby the pressurizing pump 91 or the like.

As shown in FIG. 7, in the fourth embodiment, the outside pressure(pressure in the tank 92, and also the atmospheric pressure Po when theintra-cylindrical pressure P is lower than the atmospheric pressure Po)is introduced into the cylinder. The pressure introduced into thecylinder is further increased in the compression process of the stirlingengine 10. The pressure (fluid) increased in the compression process istransferred to the crankcase 41 via the clearance CL between thecylinders 32 and 22 and the pistons 31 and 21. Thus, the crankcase 41 ispressurized.

In the fourth embodiment, at the pressurization of the crankcase 41, notonly the pressure produced by the pressurizing pump 91 works on thecrankcase 41, but the pressure produced through a further pressurizationin the compression process of the stirling engine 10 to the pressureproduced by the pressurizing pump 91 works on the crankcase 41. Hence,the reduction in energy consumption of the pressurizing pump 91 and thedownsizing of the installation scale are realized.

Next, a pressurizing of the working fluid in the working space of thestirling engine 10 and a pressurizing of the crankcase 41 according to afifth embodiment will be described with reference to FIGS. 9 and 10. Thesame structure with the embodiments described above will be indicated bythe same reference character and the detailed description thereof willnot be repeated.

As shown in FIG. 9, two check valves 76 and 77 are provided in the path71 arranged in the low temperature side cylinder 32. The check valves 76and 77 are formed so that the check valves 76 and 77 open only when apressure in an upstream side of the path 71 is higher than a pressure ina downstream side of the path 71. A piston pump 95 is arranged betweenthe check valves 76 and 77.

A crank shaft of the piston pump 95 is integrally formed with a crankshaft of the stirling engine 10 and is structured so that the movementof two pistons in the stirling engine 10 and the piston pump 95 are ofopposite phase with each other. A valve 78 is further provided on anstill upstream side of the check valve 77 in the path 71.

An upper graph in FIG. 10 represents the intra-cylindrical pressure P ofthe stirling engine 10 whereas a lower graph in FIG. 10 represents theintra-cylindrical pressure of the piston pump 95. In each graph of FIG.10, the vertical axis represents pressure and the horizontal axisrepresents crank angle.

When the valve 78 of FIG. 9 is open and the intra-cylindrical pressureof the piston pump 95 is low (or negative), the external pressure isintroduced into the cylinder of the piston pump 95 via the path 71 andis further increased in the compression process of the piston pump 95 asshown in FIG. 10.

In the compression process of the piston pump 95, the intra-cylindricalpressure P of the stirling engine 10 is in the expansion process (due tothe antiphase relation), whereby the differential pressure is large. Thefluid pressurized in the compression process of the piston pump 95 isintroduced into the cylinder when the intra-cylindrical pressure P ofthe stirling engine 10 is low (in the expansion process) and furtherpressurized in the compression process of the stirling engine 10. Thepressure (fluid) increase in the compression process is transferred tothe crankcase 41 via the clearance CL between the cylinders 32 and 22and the pistons 31 and 21. Thus, the crankcase 41 is pressurized.

As described above, in the stirling engine 10 of the fifth embodiment,the pressure of the crankcase 41 is raised up to the mean working gaspressure Pmean inside the cylinder of the stirling engine 10. Hence,when it is difficult to suppress the pressure leakage to zero throughthe perfect sealing of the crankcase 41 after the pressurization of thecrankcase 41 at the shipping, repressurization of the crankcase 41 isnecessary in some manner. Then, a pressurizing source such as the pump91 or the piston pump 95 may be necessary. These needs considered, it isadvantageous to utilize the pumping function of the stirling engine 10not simply for an original purpose such as acquisition of torque but forthe increase of the pressure of the crankcase 41 as described above inorder to minimize the installation scale/energy of the pressurizingsource.

Here, the first to the fifth embodiments can be combined as appropriate.For example, the path 81 may be provided to connect inside the cylinderand the crankcase 41 to the stirling engine of the fourth and/or thefifth embodiments as in the second or the third embodiment.

As described above, following features are disclosed according to theabove described embodiments.

(1) The crankcase is pressurized according to the change in working gaspressure in the stirling engine.

(2) In (1), the crankcase is pressurized through the intake of air fromthe outside into the cylinder in the stirling engine when theintra-cylindrical pressure P of the stirling engine is lower than theatmospheric pressure Po.

(3) In (1), the crankcase 41 is pressurized through the transfer of theintra-cylindrical pressure P to the crankcase 41 when theintra-cylindrical pressure P is higher than the pressure Pc in thecrankcase 41. The crankcase 41 is pressurized with the use of thedifferential pressure between the pressure Pc of the crankcase 41 andthe intra-cylindrical pressure P.

(4) In (2), the path to take in the air is connected to the lowtemperature side cylinder (to reduce the thermal loss).

(5) In (3), the mean working gas pressure Pmean of the working gaseventually attains the level of the pressure Pc in the crankcase 41.

(6) In (3), the mean working gas pressure Pmean is raised up to thelevel of the pressure Pc in the crankcase 41 through the closing of thepath connecting inside the cylinder with the crankcase 41.

(7) In (2), the impurities are prevented from coming into the cylinder.

(8) The pressurization of the crankcase 41 is complemented by the changein the working gas pressure of the stirling engine.

(9) In (8), the load on the device that pressurizes the crankcase 41 isreduced via the introduction of external pressure from the outside intothe cylinder when the intra-cylindrical pressure P is low.

(10) In (8) and (9), the increase of the pressure Pc of the crankcase 41is speeded up through the introduction of external pressure andpressurization by the stirling engine.

(11) With the addition of the piston which is of antiphase with thepower piston of the stirling engine for the pressurization of thecrankcase 41, the reduction of energy consumption in the pressurizationof the crankcase 41 is achieved.

(12) In one of (8) to (11), the path that introduces the externalpressure is connected to the low temperature side cylinder (for thereduction in thermal loss). In the above described embodiments, thestirling engine 10 is connected to the exhaust tube 100 to utilize theexhaust gas from the internal combustion engine of the vehicle as theheat source. The stirling engine of the present invention is, however,not limited to a type that is connected to the exhaust tube of theinternal combustion engine of the vehicle.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A stirling engine of a two-piston type in which a working gasreciprocates between a compression space which is a working space of alow-temperature side cylinder and an expansion space which is a workingspace of a high temperature side cylinder, comprising: a flow path thatcommunicates the working space of the stirling engine and outside of thestirling engine; check valves which are arranged in the flow path toallow a flow only in a direction from the outside of the stirling engineto the compression space; a valve that is arranged in the flow pathcloser to the outside of the stirling engine than the check valves; anda piston pump that is arranged between two of the check valves and cansupply pressurized working gas to the flow path, in addition to alow-temperature side piston of the low-temperature side cylinder and ahigh-temperature side piston of the high temperature side cylinder;wherein a crank shaft of the piston pump is integrally formed with acrank shaft of the stirling engine, and a phase of an intra-cylindricalpressure of the piston pump is opposite to a phase of anintra-cylindrical pressure of the sterling engine which is a combinedwave of a pressure waveform of the compression space and a pressurewaveform of the expansion space.
 2. The stirling engine according toclaim 1, wherein the flow path is provided with a filter that preventsan impurity from entering the working space from the outside into viathe flow path.
 3. The stirling engine according to claim 1, wherein theworking gas is supplied from the outside of the stirling engine into theworking space via the flow path when a pressure of the working gas inthe working space is lower than a mean value of the pressure of theworking gas in the working space in one cycle.
 4. The stirling engineaccording to claim 1, wherein a working gas of an atmospheric pressureis supplied from the outside of the stirling engine into the workingspace via the flow path.
 5. The stirling engine according to claim 1,further comprising: a communication tube that communicates the workingspace with a crankcase of the stirling engine; and an opening andclosing unit that opens and closes the communication tube, wherein theopening and the closing unit is put into a state where the communicationtube is open when the pressure of the working gas in the working spaceis higher than a pressure of the crankcase.
 6. The stirling engineaccording to claim 1, wherein the flow path is provided so that the flowpath communicates the working space at the low temperature side of thestirling engine and the outside of the stirling engine.
 7. The stirlingengine according to claim 1, wherein the low-temperature side piston andthe high-temperature side piston reciprocate, respectively, in thelow-temperature side cylinder and the high-temperature side cylinderwhile keeping each cylinder airtight with an air bearing providedbetween each cylinder and each piston.
 8. The stirling engine accordingto claim 7, further comprising an approximately linear mechanism that isconnected to each piston so that the approximately linear mechanismmakes an approximately linear motion when each piston reciprocates ineach cylinder.
 9. A hybrid system comprising: a stirling engine of atwo-piston type in which a working gas reciprocates between acompression space which is a working space of a low-temperature sidecylinder and an expansion space which is a working space of a hightemperature side cylinder, the stirling engine includes a flow path thatcommunicates the working space of the stirling engine and outside of thestirling engine, a working gas being supplied from the outside of thestirling engine to the working space via the flow path based on adifferential pressure of the working space and the outside of thestirling engine; check valves which are arranged in the flow path toallow a flow only in a direction from the outside of the stirling engineto the compression space; a valve that is arranged in the flow pathcloser to the outside of the stirling engine than the check valves; anda piston pump that is arranged between two of the check valves and cansupply pressurized working gas to the flow path, in addition to alow-temperature side piston of the low-temperature side cylinder and ahigh-temperature side piston of the high temperature side cylinder;wherein a crank shaft of the piston pump is integrally formed with acrank shaft of the stirling engine, and a phase of an intra-cylindricalpressure of the piston pump is opposite to a phase of anintra-cylindrical pressure of the sterling engine which is a combinedwave of a pressure waveform of the compression space and a pressurewaveform of the expansion space; and an internal combustion engine of avehicle, wherein the stirling engine is mounted on the vehicle and aheater of the stirling engine is provided to receive a heat from anexhaust system of the internal combustion engine.
 10. The hybrid systemaccording to claim 9, wherein the stirling engine includes a heatexchanger including a cooler, a regenerator, and the heater, wherein theheat exchanger is configured so that at least a portion of the heatexchanger forms a curve to connect the low-temperature side cylinder anda high-temperature side cylinder, and the curve is adapted to connectupper portions of the low-temperature side cylinder and ahigh-temperature side cylinder where a dimension of an inner diameter ofthe exhaust tube of the internal combustion engine is approximately samewith a distance between an end portion of the heater and an uppermostportion of the heater.
 11. The hybrid system according to claim 9,wherein the stirling engine is attached to the vehicle so that pistonsof the stirling engine reciprocate substantially horizontally.
 12. Astirling engine of a two-piston type in which a working gas reciprocatesbetween a compression space which is a working space of alow-temperature side cylinder and an expansion space which is a workingspace of a high-temperature side cylinder, comprising: a path that cancause a fluid to flow from an outside of the stirling engine to thecompression space; a check valve that is arranged in the path to allow aflow only in a direction from the outside of the stirling engine to thecompression space; a pressurizing pump that can supply pressurizedworking gas to a branch path which diverts at a position closer to thecompression space than the check valve from the path; and a tank that isarranged at a position closer to the compression space than thepressurizing pump in the branch path to store the working gaspressurized by the pressurizing pump.
 13. The stirling engine accordingto claim 12, wherein pressure of the tank or atmospheric pressure isintroduced into a cylinder which contains the compression space and theexpansion space, when an intra-cylindrical pressure of the stirlingengine which is a combined wave of a pressure waveform of thecompression space and a pressure waveform of the expansion space islower than the pressure tank.